The domain of public law can be identified by looking to a polity's constitution, legislation, and administrative regulations. All of these are public in the sense that everyone has access to them and in the sense that everyone in the polity is bound by them. Individual assent is immaterial. Contemporary justifications for public law are usually found in some sort of social contract theory. The civil government derives its authority from the consent, loosely understood, of the governed.
There are a variety of problems with the nature of what passes for public law today (it's extraordinary volume being one). There are even more problems with contractarian justifications for public law. But these problems are compounded when it comes to private law. In other words, where does the public authority find the warrant to provide state-backed sanctions for breach of private agreements?
I provided my answer in Principled Pluralism and Contract Remedies, which you can download here. My solution, however, invokes doctrines of God, the image of God in human beings, and sin, all of which are generally deemed to fall outside the scope of the sorts of "public reasons" that can be advanced in contemporary Western political discourse.
For a different approach to the "problem" of private law, go here to download Hanoch Dagan's latest piece, The Challenge of Private Law. This is the fifth time I've posted something in connection with Dagan's work. For the two most relevant to this latest post go here and here.
I regularly recur to Dagan because he regularly presents the best of liberal thinking on the topics he addresses. And it is certainly important that, even where we must ultimately part ways with a point of view, we do so only after considering the epitome of its presentation.
In any event, here is the agenda posed by Dagan:
Private law, like law more generally, is a justificatory practice: because law claims to have the legitimate authority over monopolized power in society, its carriers must always justify its prescriptions and should moreover seek to further improve the law so that it lives up to its implicit and often imperfectly executed promises. This means that an important source of law’s challenges comes from within; that at least a subset of the challenges of private law is dependent upon the value of private law. My efforts in this Essay will follow this path: I will offer a normatively attractive conception of private law and will seek to identify the challenges this conception presents to the various legal actors who participate in the evolution of private law or affect its development.For what it's worth, I think Dagan succeeds in fleshing out an autonomy-based theory of private law (which, in my opinion, is the quintessential liberal theory) with due recognition of the contemporary social context and innately social character of human beings:
Private law – either common law or equity; judge‐made law or statutory – establishes ideal frameworks for respectful interaction between self‐determining individuals,which are indispensable for a society where all recognize one another as genuinely free and equal agents. Only private law – the law of our interpersonal (horizontal) relationships – can form and sustain the variety of frameworks necessary for our ability to lead our chosen conception of life.What Dagan does not address, and which liberalism alone cannot justify, is why we should care about "respectful" interaction, how and what it means to be "genuinely free," and in what senses we are (and are not) "equal." I am all for respect, freedom and equality but fail to see how even a nuanced approach like Dagan's makes recognition of such virtues obligatory.
To be fair to Dagan, he posits only that such commitments are what constitutes the current liberal order; he does not presume to address the ontological foundation of that order. That said, Dagan's piece is excellent. He acknowledges the indispensability of private law for human flourishing as well as the pedagogy toward maturity that a wide space for private law affords. Moreover, Dagan's integration of concerns for material equality into the substance of private law should also give pause to those who reflexively commit only to formal equality as the ne plus ultra of private law.